Dental caries is a disease that frequently occurs soon after teeth erupt into the oral cavity, an environment that is generally hostile to the teeth of most individuals. Sites particularly prone to caries development are the occlusal surfaces of the posterior teeth. This is largely because these surfaces possess a morphology (i.e. pits, fissures and fossae) that favors retention of both fermentable carbohydrate and bacterial biofilms. These two entities are primary elements in dental caries causation. Combined, they result in the production of the acid that leads to tooth demineralization and the initiation and development of dental caries lesions. More tooth decay occurs in occlusal locations and to lesser degree in interproximal dentition sites (where teeth are in contact with one another) than elsewhere in the human dentition. This is because bacteria and fermentable carbohydrate collect more easily there, and are protected from the caries inhibiting effects of saliva, than occurs in other more salivary accessible dentition locations.
Dental caries begins as a demineralization process which leads to the development of pores and tunnels through the protective, non-electrically conductive enamel (Longbottom, C. and Huysmans, M.C.D.N.J.M. Electric measurements for use in caries clinical trials. Caries Res. 29, 94-99, 1995. Longbottom C and Huysmans M.C.D.N.J.M. Electrical measurements for use in caries clinical trials. J. Dent. Res. 83 (Spec. Issue C) C76-C79, 2004). Continued demineralization eventually results in enamel breaching. Once the enamel is breached, caries advances and spreads rapidly through the underlying dentine, a tissue much less mineralized than enamel. Such spreading is made easy because dentine is traversed by numerous tubules. Many, if not most of these dentinal tubules, especially in younger teeth, reach all the way to the dental pulp (Pashley D. H. Theory of dentin sensitivity. J. Clin. Dent. 5:65-67, 1994).
Non-cavitated caries lesions, particularly in the pits, fissures and fossae of the posterior teeth are difficult to detect and assess in humans. Teeth mainly involved include the first and second primary molars and the premolars and molars of the permanent dentition. These teeth and interproximal dentition sites are where the majority of dental cavities occur.
Presently, detection of caries development is mostly done by a dentist or other dental care provider with a simple, pick-like device, generally referred to as a dental explorer. Such detection is performed by visual examination for indications of mineral loss, and is done with or without x-rays. None of these tools is suitable for detection of a high percentage of non-cavitated occlusal caries lesions even when there is caries penetration into the dentine. Many of these early developing caries lesions are not cavitated, but do involve extensive tunneling through the enamel and such tunneling may not be detectable. Such caries development is frequently hard to discover until destruction of tooth substance becomes more substantial and the dentine becomes progressively more and more involved. As a consequence of the difficulty of their discovery, these lesions are commonly referred to as hidden dental caries (Weerheijm K L, van Amerongen W E, and Eggink C O. The clinical diagnosis of occlusal caries: A problem. J. Dent. Child. 56, 196-200, 1989). Their early discovery is often missed or involves much uncertainty. Not surprisingly, there is opportunity for pulpal damage to occur and for teeth to be lost unnecessarily (Verdonschot E. H., Wenzel A., Truin G. J. and Konig K. G. Performance of electrical resistance measurements adjunct to visual inspection in the early diagnosis of occlusal caries. J. Dent. 21: 332-337, 1993). Ironically, the anti-caries agent, fluoride, can be detrimental to early detection, because it favors less cavitation (Hudson P. and Kutsch V. K. Microdentistry: Current pit and fissure caries management. Compendium 22: 469-483, 2001). This is because fluoride reduces the solubility of the enamel covering the dentine, thereby enabling the enamel to remain largely intact while underlying dentine continues to be demineralized (Lussi A., Firestone A., Schoenberg V., Hotz P., and Stich H. In vivo diagnosis of fissure caries using a new electrical resistance monitor. Caries Res. 29: 81-87, 1995). For these reasons, it has become very important that caries lesions be detected as early and as easily as possible.
Because the enamel of freshly erupted teeth commonly exhibit a certain degree of porosity, such teeth are more prone to dental caries development than if they had been exposed in the mouth for an extended period under non-cavity producing and mineralizing conditions. Such improvement is called maturation and occurs because many of these exposed teeth acquire calcium and phosphate ions from saliva along with various proteinaceous accretions. These changes involve increased enamel mineralization, reduced enamel permeability and greater caries resistance. This is helped by fluoride if applied or taken up naturally during the tooth maturation process (Ie Y. L., Verdonschot E. H., Schaeken, M. J. M. and vant H of M. A. Electrical conductance of fissure enamel in recently erupted molar teeth as related to caries status. Caries Res. 29: 94-99, 1995). In contrast, in a caries-prone mouth where a demineralization environment is present, an opposite result occurs more readily, i.e. development of increased porosity and cavitation.
Several approaches have been unsuccessfully used to detect dental caries in its early stages. One of these involves testing for a tooth's ability to conduct electrical current even when there is no visible tooth mineral loss from the enamel and no cavitation can be seen. Electrical resistance is associated with the presence of intact, non-demineralized enamel; but, as a caries lesion develops and enamel mineral is progressively lost, fluid can seep therein and electrical resistance of the enamel correspondingly and progressively decreases (Williams, D. L., Tsamtsouris A., and White, G. E. Electrical resistance correlation with tactile examination on occlusal surfaces. J. Dent. Res. 57: 31-35, 1978, Longbottom C and Huysmans M.C.D.N.J.M. Electrical measurements for use in caries clinical trials. J. Dent. Res. 83 (Spec. Issue C) C76-C79, 2004).
Breaching of enamel occurs more easily in occlusal pit and fissure sites. As noted above, these dentition locations are where continual presence of acidogenic bacteria and fermentable carbohydrate can undergo significant and continual interaction. This favors prolonged generation of acid and in turn, prolonged and extensive tooth demineralization. As this happens, a point is reached where the enamel is sufficiently demineralized and porous that saliva penetrates therethrough and because of the ions that saliva contains, flow of electrical current can take place as a result. The more extensive the demineralization, the more readily these events occur and the easier it is to detect caries lesion development.
Earlier investigators measured electrical resistance or conductivity with direct current devices to determine if a tooth had lost mineral and had become carious (Pincus, P. A new method of examination of molar tooth grooves for the presence of dental caries. J. Physiol 113: 13-14, 1951. Mumford, J. M. Relationship between the electrical resistance of human teeth and the presence and extent of dental caries. Brit. Dent. J. 100, 239-244, 1956. Mayuzumi, Y, Suzuki, K and Sunada, J. A method of diagnosing incipient caries in pits and fissures by measuring electrical resistance. J. Dent. Res. 43, 431, 1964. Takeuchi, M., Kizu, T., Shimizu, T., Eto, M. and Amano, F. Sealing of the pit and fissure with resin adhesive. II. Results of nine months' field work, an investigation of electrical conductivity of teeth. Bull Tokyo Dent Coll 7, 60-71, 1966. Williams, D. L., Tsamtsouris A., and White, G. E. Electrical resistance correlation with tactile examination on occlusal surfaces. J. Dent. Res. 57: 31-35, 1978). Others subsequently used alternating current and measured impedance to do essentially the same thing White G. E., Tsamtsouris A., and Williams D. L. A longitudinal study of electronic detection of occlusal caries. J. Pedod. 5, 191-201, 1981. Pitts N. B. Clinical diagnosis of dental caries: a European perspective J. Dent. Educ. 65: 972-978, 2001). In each case, a cavity detecting device was provided, including a measuring probe made of a conducting metal, a direct or alternating current source, a resistance source, an impedance or conductance detector, and a reference electrode suitable for application, generally by attachment to a non-oral soft tissue part of the body. The human body is sufficiently conductive electrically to enable complete electrical continuity via the body between the measuring probe (i.e. the indicator electrode) and a reference electrode usually attached by adhesive means to a body surface such as the ventral surface of the forearm or the back of the neck or by means of a metal hook, the end of which is immersed in the mouth saliva usually by curling around the lower lip.
Tooth enamel is electrically non-conductive unless it is breached by demineralization or fracture. When this occurs, fluid at or entering the breached enamel site enables completion of an electrical circuit that allows current to flow. The electrical current used may be as low as a few micro-amperes (μA) in magnitude. Hence, it is safe even for use in medically compromised patients. In addition, the procedure is painless.
It has previously been found that special precautions have to be taken while making measurements to ensure electrical continuity without causing any peripheral electrical conductance to saliva or other moisture on the tooth or to saliva or other conductance means elsewhere in the mouth. Such isolation of the measuring electrode from surrounding saliva is an absolute requirement for success. Complete isolation can be achieved by using a rubber dam (Williams, D. L., Tsamtsouris A., and White, G. E. Electrical resistance correlation with tactile examination on occlusal surfaces. J. Dent. Res. 57: 31-35, 1978). However, such use of a dam is cumbersome and is not practical when an extensive mouth examination is required. Instead, most investigators have used a stream of air from an air syringe in an attempt to dry the tooth around but not at the measuring site. To do this simply, consistently and rapidly has been a major problem.
Ricketts et al. used a stream of air surrounding the measuring electrode to isolate the measuring site from surrounding surface electrical conduction (Ricketts, D. N. J. Kidd, E. A. M., and Wilson, R. F. A re-evaluation of electrical resistance measurements for the diagnosis of occlusal caries. Brit. Dent. J. 178: 11-17, 1995). However, the large size of the measuring tips used by these investigators prevented accurate measurements. Further, such large tips, with their drying feature, were not suitably shaped or sized for many of the sites that required more effective probing.
Current methods often yield false and/or variable readings. Current methods also lack the ability to rapidly and consistently detect non-cavitated caries lesions early and accurately. Basically, detection of non-cavitated caries lesions requires electrical linkage between the measuring electrode at the enamel surface measuring site and fluid within the caries lesion. Detection also requires the absence of any electrical conductance immediately around the lesion site. Furthermore, a method of instantly knowing that detection is operating properly is necessary.